Workers at Montreal's Palais des congrès had to clean paint off the windows of the convention centre after the building was defaced by anti-Plan Nord slogans.
Paint was splashed and anti-Plan Nord posters were pasted to the windows of the Montreal convention centre overnight ahead of the Board of Trade's Strategic Forum on Natural Resources.
"Non Plan Mort" — or "No to Plan Death" — was also sprayed on the windows.
Plan Nord is the provincial government's plan to develop natural resources in Quebec's north.
The demonstration began before the 7:30 a.m. convening of the forum on natural resources.
Of the dozen or so protesters, four were detained by police.
Two of them, a 28-year-old man and a 19-year-old woman, face charges for disturbing the peace.
Another two men, a 28-year-old and a 22-year-old face charges of armed assault.